This invention relates to composite reinforced structures, and, more particularly, to facesheets for stiffening metallic honeycombs.
Structural materials used in spacecraft and structures built in space must be stiff, strong, and extremely lightweight. The cost of raising one pound of weight from the earth to orbit is many thousands of dollars, and therefore great savings and increased payloads can be secured by precisely engineering structural materials to meet the required mechanical properties with minimum weight.
In some spacecraft applications, high structural stiffness at particular locations is required. Structural vibrations are induced in the spacecraft structural components. The amplitudes of the vibrations are dependent upon their frequencies, which in turn depend in part upon the stiffness of the structure. If the amplitudes become too high they can destroy the structure. The stiffness can be expressed in terms of the modulus of elasticity, a material property defined as the elastic stress divided by the elastic strain. To control the vibrations, the stiffness of the structure can be precisely controlled, within the limitation that the weight must be minimized.
Many spacecraft utilize solar cells for generating electrical power. The solar cells for typically thin plates that must be mounted upon an underlying solar panel structure for support. One approach to fabricating the underlying solar panel structure is to use a lightweight aluminum honeycomb substrate with a facesheet bonded to the open end of the honeycomb to stiffen the honeycomb and to receive the solar cells. Such a material can be tailored to a specific stiffness that is resistant to development of destructive vibrations in solar panels.
The aluminum honeycomb material is fabricated to a repeating cellular morphology similar to that of the familiar honeycomb of honeybees, except that the cell walls of the manmade material are of aluminum or other lightweight material. The cell walls are arranged in a hexagonal cellular pattern for geometric compatibility and strength. Typically, the cell walls are a lighweeight aluminum alloy such as 5056 aluminum about 0.0007 inches thick, and the maximum cross sectional dimension of each cell is about 3/8 inch. Such materials are commercially available in various thicknesses, and 1/2 inch thick pieces are often used in spacecraft solar panel construction.
The facesheet can be any of several materials. Most commonly, the facesheet is a tightly woven fabric of a synthetic fiber, such as Kevlar, having a high modulus of elasticity so that the facesheet and the honeycomb/facesheet structure are stiffened. While such structures do provide the necessary support and high stiffness, it would be desirable to find an alternative approach to the support structure that would have equivalent or improved structural properties, with even lower weight.
Accordingly, there exists a need for an improved lightweight structural material having high, controllable stiffness, dimensional stability, and reduced weight compared with existing materials. The structural material must be compatible with existing approaches to the mounting of the solar cells and their use, in the preferred application. More generally, the structural material would desirably be operable in a variety of spacecraft applications. The present invention fulfills this need, and further provides related advantages.